Valve means with built in dashpot



Aug. 7, 1956 .w. A. HUNTER 2,757,643

VALVE MEANS WITH BUILT IN DASHPOT Filed Aug. 9, 1951 2 Sheets-Sheet lINVEN TOR.

,7MLLW/W 2 Sheets-Sheet 2 W. A. HUNTER VALVE MEANS WITH BUILT IN DASHPOTAug. '7, 1956 Filed Aug. 9, 1951 United States Patent VALVE MEANS WITHBUILT IN DASHPOT William A. Hunter, Highland Park, Mich., assignor toChrysler Corporation, Highland Park, Mich, a corporation of DelawareApplication August 9, 1951, Serial No. 241,025

7 Claims. (Cl. 121-465) This application relates to a valve system whichis characteristically quiet in operation in the presence of the usua1outside disturbances, and particularly to such a valve system for use inan hydraulic steering mechanism for vehicles.

Hydraulic steering mechanisms for vehicles conventionally include suchelements as a power cylinder or fluid motor by means of which thevehicle running gear linkage is operated to steer the vehicle, a sourcefor pressure fluid which is delivered to the power cylinder or motor, avalve unit serving the power cylinder or motor and controlling flow ofthe pressure fluid so delivered, and a control valve operating membercommonly connected to the vehicle steering wheel and directly orindirectly mechanically connected to the running gear steering linkage.One common expedient is to have the latter control valve operatingmember interposed as a reaction member in the mechanical train betweensteering wheel and running gear steering linkage.

It has been noticeable in certain hydraulic systems, especially systemssuch as the above hydraulic power steering type, that the road reactiondue to vehicle motion has a tendency to be fed into the vehicle runninggear and that by following along a direct or indirect mechanical path tothe valve operating member the impacts of road reaction tend to bereflected in valve clatter in the power cylinder control valve unit.Disturbances which have a tendency to produce valve clatter are not onlyobjectionable because of their effects primary in nature, but also arefurther objectionable because of their secondary feed back effects ofthe character in which the disturbed control valves cause the powercylinder to be set spasmodically in motion and to produce accumulativedynamic disturbances which may feed back into the already disturbedmechanical path just noted.

An object of the present invention is to provide a valvemember-operatedvalve unit having a damping 'device incorporated therewith to oppose thesudden motions of the valve operating member which give rise to valveclatter.

A further object is to provide the combination of a pair of opposedvalves having an intervening reciprocal valve operating member, in whichcombination both valves readily move when the operating member is set inslow motion in either direction of reciprocation but in which more rapidmotion of the valve operating member in one direction of reciprocationis forcefully opposed by one valve and in the opposite direction ofreciprocation is forcefully opposed by the other valve.

Another object of the invention is the provision of areciprocating-member-operated type of valve formed of fixed and movablesleeve-like parts one within the other, the valve being operated at oneend due to thrust of the reciprocating member on the movable sleeve-likepart and having a dashpot at the other end self-contained between thesleeves to react against and oppose thrust from the reciprocatingmember.

Other features, objects, and advantages will either be specificallypointed out or become apparent when for a Patented Aug. 7, 1956 Figure 2is a perspective view showing the prime power and steering machinery ofthe vehicle of Figure 1;

Figure 3 is a plan view partly in section showing the steering valvesand steering motor incorporated in the steering machinery of Figure 2;

Figure 4 is an enlarged sectional view of one of the individual valvesof Figure 3; and Figures 5 and 6 are sections through modified forms ofthe valve of Figure 4.

In Figure l of the drawings, a steerable vehicle is; shown having a bodyframe or chassis 10 characterized by suitable running gear providingspring suspension for the vehicle, front and rear. A pair of rear wheels12 having an interposed drive differential 14 is carried on either sideof the chassis 10 by the outer ends of an axle housing 15 which isattached to intermediate portions of longitudinal rear load springs 16.The ends of springs 16 are connected to the chassis 10 for springing therear of the vehicle.

A pair of front wheels 18 is disposed on either side of the front end ofthe vehicle chassis 10 at the outer ends! of the respective similarsteering knuckles shown, only one of which at 20 will be described inthe environment of its front suspension unit for the reason of brevity.

Knuckle 20 is pivoted about a vertically extending knuckle support 21which is mounted at the laterally outer ends of a pair of verticallyspaced control arms 22. The control arms 22 are pivotally connected attheir inner ends to locations on a cross member 24 of the chassis 10.The steering knuckle 20 has a steering arm 26 aifixed thereto andextending rearwardly. A steering intermediate arm 28 is pivoted at 30 tothe cross member 24 and has a forked end to which is attached a pair oftie rods 32 which extend in opposite directions and one of which isconnected to the rear end of the knuckle arm 26. The other tie rod 32 issimilarly connected to another knuckle arm symmetrically arranged to thevehicle chassis with respect to knuckle arm 26. The intermediate arm 28has another end which is pivoted at 36 to a longitudinally extendingdrag link 34. The drag link 34 is pivoted at its rear end to adownwardly hanging pitman 38 carried on a steering shaft laterallyprojecting from a power cylinder unit 40. A vehicle engine 42 issupported at its forward end by motor mountings to the chassis crossmember 24. I

In Figure 2, the engine 42 may be seen to have a crankshaft 46 which bya V-belt provided at 44 drives a water circulating pump 48 for theengine. The water pump 48 in'turn drives a V-belt 50'for a generator 52.A reservoir 54 and oil pump assembly 56 is mounted at the rear of thegenerator 52. A replaceable cartridge type full flow filter element, notshown, is located in the reservoir 54. Oil being returned to reservoir54 from the hydraulic system later to be described, passes through thefull flow oil filter and into the reservoir chamber. A small springloaded vent valve provided in the reservoir cover is forced open toprovide a passage to the atmosphere when excessive pressure occurswithin the reserbuilds up and in the illustrated embodiment was set tounseat at about 5 to 7 pounds pressure to permit oil to 3 pass by thefilter and directly into the chamber of reservoir 54.

Oil pump 56 is a rotor type pump driven from the rear end of thegenerator shaft 52 by means of a flexible coupling, not shown. Rotormeans provided in the pump 56 draws oil from reservoir 54 and dischargesit through certain flow control means to supply the above notedhydraulic system. Oil pressure in the hydraulic system is determined bythe resistance to turning of the front road wheels 18. A rapid build-upof oil pressure tends to occur when the road wheels 18 are turnedagainst a curb or when the steering wheel is turned all the way in onedirection such that the power steering mechanism reaches the end of thestroke. To prevent excessive oil pressure, a pressure relief in pump 56is provided to limit the oil pressure to between 600 to 650 pounds persquare inch. During a normal parking operation of the vehicle shown, theoil pressure averaged about 500 pounds per square inch.

The pump 56 supplies pressure fluid for the power cylinder unit havingan axially aligned pair of opposed pistons 58 reciprocable therein andeach carrying an inner protruding stud 55 at their relatively adjacentends. Other main elements of the compact power steering unit disclosedin Figure 2 in conjunction with the engine 42 comprise a steering gearshaft 62, a worm and roller drive 64, 66, a lower section or piece 80 ofa two-piece steering column incorporating a universal joint 73 at anin-between location and an upper piece 74, a

valve body assembly 82, and a pair of jointly meshing spur gears 70, 72.The power cylinder unit 40 is formed of a pair of drawn steel cylinders57 which are screwed into a steering gear housing 59 and locked intoplace each with an appropriate spanner nut 61. The inner protrudingstuds 55 carried by pistons 58 are in actuality hardened steel pinswhich bear against a hardened steel roller shown carried on a power arm60. To insure accurate movement of the power arm 60 the hardened steelroller may be mounted on needle bearings. The power arm 60 is mounted tosteering gear shaft 62 and may be held in position by a set screw andlock nut. A series of broached splines, not shown, on the side oppositethe set screw positively locks the power arm 60 to the steering gearshaft 62. The worm 66 is mounted for rotation by means of a worm shaft68 having a longitudinal axis 67. The worm 66 meshes with roller 64which is carried by the steering gear shaft 62 and by means of which arocking movement may be imparted to the shaft 62.

The spur gear 72 meshing with the worm shaft spur 70 is carried by thelower piece 80 of the noted twopiece steering column. Lower piece 80,which through universal joint 73 actually forms an extension of thesteering column, is rotatably supported in a case-mounted sphericalbearing 75, which permits the steering column spur gear 72 to orbitslightly about the work shaft spur 70 and thus climb up or down withrespect to work shaft axis 67. The lower piece 80 of the steering.column extendstthrough the valve body assembly 82. Valve body assembly82 is served with pressure fluid by a.flexible supply line 84 from thepump 56 and by a flexible return line 86 leading to the reservoir 54.The upper piece or steering shaft 74 of the two-piece steering column isrotatably mounted within a column jacket 78 and is rotatable by aconventional steering wheel 76. The power cylinders 40 have respectiveinlet lines 94 coming from the valve body assembly 82 and outlet lines96 leading back to the valve body assemby.

In Figure 3 the system supply line 84 from pump 56 is connected to thevalve body assembly 82 and supplies an oil gallery 88 communicating withupper and lower annular chambers, one of which is shown at 90. The valvebody assembly includes four valves, two jointly opposed valves on theleft acting as distribution valves, and two jointly opposed valves onthe right acting as reaction valves, all of which may be made alike. Forconvenience of manufacture, the respective distribution and reactionvalves 100 are disposed somewhat difierently in the hydraulic systemwith respect to one another and have different purposes in theiroperation. Of the opposed distribution valves to the left, the upper onecontrols the annular chamber 90 and provides an appropriate restrictiveconnection therewith to a chamber 92 in communication with one or theother of the power cylinders 40, and the lower opposed distributingvalve is connected similarly to the remaining power cylinder 40. Theseconnections to the respective ends of the power cylinders 40 areprovided by the power cylinder inlet lines 94 shown in Figure 2. Thepower cylinder outlet lines 96 in turn connect the same respective endsof the power cylinders to annular chambers, one of which is shown at 97,for the opposed reaction valves to the right in Figure 2. The fluidpassing through the upper reaction valve, for instance, is controlled bythe valve and thence delivered to an annular chamber 98 where upon it isdischarged into a valve block assembly internal chamber 103 which isconnected with the system return line 86 draining back to reservoir 54.

Each valve 100 of the four-valve body assembly is suitably sealed byO-ring seals as at 102. The ditference between the pairs of opposedvalves described is one of function, the so-called distribution valveson the left serving to direct oil to the proper cylinder whereas thereaction valves to the right do two things: control the oil flow fromand back pressure in the power cylinders and also regulate the ratiobetween manual and hydraulic steering torque in an inherent manner whichmay become apparent with close study of the hydraulics of the system. Inthe valve body assembly chamber 103, there is located a valve operatingblock 104 through which the steering shaft extends journalled therein byneedle bearings 106. An eccentric cam 108 provides for adjustment of thevalve operating block 104 according to a predetermined path.

In Figure 4 one of the identical four valves 100, shown in Figure 3, isillustrated in enlarged cross sec tion. Valve 100 has an outer partcomprising a sleeve 109 open at one end and closed at the other. Theinner part of the valve includes a valve proper 110, a seat 130 for aspring, a spring 124, and a ball 134 all of which are assembled in acombination movable as a unit with respect to the outer part 109. Fromeither the chamber of Figure 3 or the chamber 97 of Figure 3, dependingon whether the valve is connected to act as a distribution or a reactionvalve, oil enters an internal passage 111 in valve of Figure 4 throughone or more holes 112, preferably four in number, around thecircumference of the sleeve and four holes 114 in the sleeveconstituting the valve proper. When the valve is open, the oil flows ina direct fashion from the valve sleeve inlet holes 112 through a set ofeight discharge holes 116 in the sleeve 109 and also in a morecircuitous path from the inside 111 of the valve through two sets 118,120 of eight holes each in the valve proper and in'the valve sleeve 109.Sleeve 109 is provided with suitable annular grooves 122 in which theO-rings of Figure 3 are received.

A spring 124 occupies a dashpot chamber 126 formed by the dashpotportion of valve proper 110 and the closed end of sleeve 109. Dashpotportion .125 has an opening 128 formed therein to provide controlledleakage between dashpot chamber 126 and the hydraulic circuit at 112.The seat 130 for spring 124 is provided with one or more apertures 13?.and serves as the upper part of a cage for the ball check valve 134.Ball check valve 134 seats in an opening 136 forming the mouth ofpassage 111 and thereby restricts the opening 136. Ball 134 unseats topermit unrestrained downward movement of valve proper 110 but seats,however, in its full capacity as a. check valve upon upward movement ofvalve proper 110 and effectually traps fluid in the dashpot chamber 126.The controlled leakage permitted by bleed 128 from chamber 126 permitsonly slow movement of the valve proper 110 in an upward direction asshown in Figure 4. The fit between dashpot portion 125 and sleeve 109 inthe vicinity of bleed 128 is loose enough for bleed 128 to be calibratedand to function as intended. Spring 124 urges the valve proper 110 in adownward direction at all times.

The operation of the dashpot construction just set forth is bestunderstood from a brief description of the hydraulic system operation.When the engine 42 is running and the steering wheel is not turned, oilfrom pump 56 flows through flexible hose 84 to the gallery 88 in thevalve body assembly and from there to the respective ones of thedistributing valve annular chambers including chamber 96 The oil thenpasses from the distributing valves and in the case of the upperdistributing valve, for instance, through a discharge passage 92 in thevalve body and through rigid inlet tubing 94 to one of the respectivepower cylinders 46. From the power cylinders 40 the oil passes throughrigid outlet tubing 96 and reenters the valve body housing and flows tothe respective annular chambers including the upper annular chamber 97,for the reaction valves on the respective opposite sides of the valveoperating block 104. Passages in the valve and valve body provide forthe transfer of oil from each reaction valve to an annular chambersimilar to annular chamber 98 for the upper reaction valve and thence tothe valve operating block cavity 163. From block cavity 163 oil flowsthrough flexible hose 86 to the reservoir 54. When the steering wheel 76is turned, the valve operating block 104 closes the set of valves towardwhich the block moves and permits the opposite set fully to open.

The fluid coming to the inlet of one of the opposed pistons 58 is shutoff and the fluid leaving through the outlet of the opposite piston 58is shut off; oil flow then occurs only through the open set ofdistribution and reaction valves and the pistons 58 are caused to movein the power cylinders 40. Only about .007-.013 inch movement at valveblock 104 is required in the physical embodiment of the structure shownin order to start application of the hydraulic power. The spring 124insures positive contact between the valve proper 110 and the valveoperating block 104. When the ball 134 Seals the small dashpot chamber126 in the rear of the valve, a dashpot action is provided because theonly oil exit from this chamber is the small hole 128 and therefore, thevalve operating mechanism tends to be prevented from clattering whenroad shocks are encountered.

It has been previously noted that the lower end 80 of the two-piecesteering column is connected to the upper piece 74 by a universal joint73 and is mounted in a spherical bearing 75, such mounting permittingthe steering column spur gear 72 to move several thousandths of an inchwith respect to the spur gear 70 and the worm shaft axis 67. Theeccentric cam 108 adjustment is used to control center spacing of thespur gears 70, 72 and to prevent lateral movement of the steering columnspur gear 72. Therefore, when the steering wheel is turnedcounterclockwise or clockwise, the steering column spur gear 72 climbsup or down with respect to worm shaft axis 67. The resulting movement ofthe valve operating block 104, while of very small magnitude, issuflicient to open and close the distribution and reaction valves 100 inthe desired combination. A difference in pressure occurs between thepower cylinders when the valves are operated and the pistons 58 move thepower arm 60 in the same direction as do the worm and roller 64, 66 indriving the steering gear shaft 62.

During neutral operation when the steering wheel 76 is not turned, allfour valves 106 are in a partially open position which at least for theupper set of valves is brought out in the sectioned showing of Figure 3.Oil

from the pump 56 flows through each distribution valve through lines 94to a respective power cylinder 40 and from there through one of thelines 96 to the corresponding reaction valve to the right in Figure 3.Oil is returned from each reaction valve through a flexible line 86 tothe oil reservoir and filter 54. same oil pressure is supplied to bothcylinders 40, the pistons remain in a stationary position and there isno amount of steering movement of the front road wheels 18. When thesteering wheel 76 is turned for a left turn, for instance, the steeringcolumn spur gear 72 climbs up the worm shaft spur gear 70 in an orbitalfashion and the valve operating block 104 moves up to cause the topvalves to move toward fully closed position and the bottom valves 100 tomove toward fully open position. happen to be the valves selected whichfor purposes of the present example are to be visualized in the fullyclosed position and but very slight movement is required to change thevalves from the neutral position shown (i. e., partially open) to aclosed position. Oil from pump 56 will then flow at an increased ratethrough the resultingly fully open lower distribution valve to one powercylinder 46. Due to the fact that the open reaction valve is in theoutlet line 96 from the opposite power cylinder 40, a difference inpressure occurs between the two cylinders, and the piston assemblies 53are moved in the direction of the low pressure end of the cylinderassembly.

Piston movement is transmitted to the steering gear shaft 62 throughpower arm 60 and thus adds to the manual effort supplied to the steeringgear shaft 62 through worm and roller 64, 66. The resultant rotation ofthe steering gear shaft 62 tends to turn the worm shaft spur gear 70 toan additional degree than does the rotation alone provided by thesteering wheel movement. As a result, the steering column spur gear 72and valve operating block 104 are forced back into the neutral positionand the road wheels are maintained in the position indicated 'by thesteering wheel location. The hydraulic system disclosed also reacts tooppose any tendency of the road wheels to turn due to chuck holes, ruts,or a tire blow-out. When the wheels tend to turn as a result of roadobstruction or blow-out, the movement is transmitted through the runninggear steering linkage 26, 32, 28, 34, 38, 62 to the worm and roller 64,66. Because the driver is holding the steering Wheel 76 the resultantrotation of the Worm shaft spur gear 70 forces the steering column spurgear 72 to move up or down. This movement causes one set of distributionand reaction valves to open, and the other set on the opposite side ofblock 104 to close such that the oil pressure in the power cylinders 40opposes the movement of the a car wheels. Because the action of thehydraulic system is essentially instantaneous, very little wheel fightis felt by the driver.

The movement of the steering column spur gear 72 up and down, as justdescribed, is not attended by any objectionable valve clatter by reasonfirst, of the fact that there is no valve lost motion to take up owingto presence of spring 124, and second, due to the fact that the dashpotchambers 126 of two of the valves 100 are always efiective to oppose theblock 104 being suddenly set in motion from the neutral position of restand cansing an attendant clatter. When the vehicle is turning a corner,the car wheels automatically seek to return to a straight ahead positionand center themselves as soon as the driver releases the steering Wheel.This self-centering action of the wheels occurs in the same fashion aswith conventional mechanical steering because the driver is not applyingthe small amount of effort required to hold the wheels in a turnposition.

In the modification of Figure 5 a valve 200 is shown which is eithervery similar or the same in operation as the valve of Figure 4 but whichdiffers slightly there- Inasmuch as the The sectioned set of valves ofFigure 3 from in regard to structure. The outer part of the valve 200 isconstituted by a sleeve 209 closed at one end and open at the other end.The inner part of the valve is constituted by a valve proper 210, a seat230 for a spring and a ball check, a ball check 234, and springs 224,242 all of which are assembled in combination to move as a unit withrespect to the outer valve part 209. Outer part 209 and valve proper 210are provided with sets of four and eight passages similar to the valveof Figure 4 and have annular grooves 222 suitable for O-ring seals.Valve proper 210 has an internal passage 211 and a dashpot portion 225.Dashpot portion 225 slides in the closed end of sleeve 209 and isslightly undersized with respect to the inside diameter of sleeve 209such as to provide controlled leakage between the sliding surface. Theball check seat 230 has an opening 236 to the internal passage 211 andin the opening is received the ball check 234 so as to restrict it. Alight spring 242 located in a dashpot chamber 226, acts to hold ballcheck 234 on its seat and a surrounding heavier spring 224 located indashpot chamber 226 acts on seat 230 to urge the valve proper 210 in adownward direction at all times. Upon upward movement of valve proper210 within sleeve 209, ball check 234 seats and restricts flow out ofdashpot chamber 226 permitting the valve to move only slowly as fluidescapes between the sliding dashpot portion 225 and the adjacent innersurfaces of closed end of sleeve 209.

In Figure 6 another modified form of valve is shown at 300 similar tothe valve of Figure 4. A sleeve 309 constitutes the outer part of valve300 and is closed at one end and open at the other. The inner part ofvalve 300 is constituted by a valve proper 310, a ball check 334,springs 324, 342, and a seat 339 for a spring and ball check andproviding at the same time a dashpot portion, all assembled together incombination to move as a unit with respect to the outer valve part 309.Valve part 309 is provided with sets of four and eight passages similarto the valve of Figure 4 and with suitable annular O-n'ng grooves 322which are similarly shown. Valve proper 310 is slotted with longitudinalslots 344 at one end which define one or more protruding fingers 346,preferably four in number. Fingers 346 engage an end of seat 339 inwhich an opening 336 is provided which leads into an internal passage311 in valve proper 310. The ball check 334 seats in the opening 336 toclose it and restrict flow from a dashpot chamber 326 formed betweendashpot portion 340 and the closed end of sleeve 309. The ball check 334is urged toward seating position by a light spring 342. A relativelyheavier spring 324 thrusts against seat 339. The seat 339 is providedwith a restricted opening 328 which is open at both ends in the positionshown for the valve in Figure 6. As valve 310 is moved upwardly, theouter end of opening 328 is covered by the adjacent inner surface of theclosed end of sleeve 309 and provides by virtue of the sliding fitbetween surfaces an even greater restricted bleed for the dashpotchamber 326. When ball check 324 is seated it restricts the centralopening 336 into passage 311.

Valve 100 of Figure 4 and the modifications thereof at 200 and 300 inFigures 5 and 6 are each of a type adapted to use in the valve bodyassembly 82 of Figure 3.

Variations within the spirit and scope of the described invention areequally comprehended by the foregoing description.

What is claimed is:

1. For use with a mechanically operated member subject to shock andhaving two sides and an hydraulic circuit system; a valve forming a partof said circuit system and incorporating a self-contained dashpottherein for damping movements of the mechanically operated member, saidvalve being formed of parts mounted one within the other and oneprojecting axially outwardly of the other for establishing engagementwith one side of the mechanically operated member, means for biasingsaid projecting part into continuously engaged relation with the saidone side of the mechanically operated memher and opposing all relativelyinward movement of the projecting part due to urgings of the said oneside of the mechanically operated member, the parts being relativelyreciproeative and the outer part thereof having a plurality of firstports and a second port, said plurality of first ports being in line ofthe inner part reciprocation with respect to the outer part so as to beeffectively controlled by the inner part, said parts forming afluid-trapping dashpot container as aforesaid at an end thereofdecreasing in volume with the movement aforesaid due to the urgings ofthe mechanically operated member and having an opening incorporated inthe inner part and connected with the hydraulic circuit, a spring biasedvalve element covering the opening to prevent rapid escape of hydraulicfluid trapped in the container upon decrease in volume of the same andthereby to effect resistance to the urgings of the mechanically operatedmember and damp the inward movements of the said one side thereof, and asimilar valve engageable with the other side of the mechanicallyoperated member.

2. A controlmember-actuated valve having slow response to displacingforces transmitted thereto by such control member, said valve beingformed of sleevelike parts mounted one within another with an annuiarspace between and being relatively disposed. such that one part projectsbeyond the other for engagement with the control member and isrcciprocable with respect to the said other part, said parts forming afluid-trapping damping container at one end changing in volume withrelative reciprocal movement of the parts, the inner of the sleevelikeparts having an opening between the interior thereof and the annularspace and between the interior thereof and the container, said valveparts having ported valving surfaces formed thereon communicating withthe annular space and interior of the inner part and registerable uponreciprocation of the parts to permit discharge of hydraulic liquidtherefrom, and a spring-biased valve element inside the sleeve-likeinner valve part and covering the container opening to prevent rapidescape of hydraulic liquid trapped in the container thereby causing theinner valve part to respond slowly to displacing forces transmittedthereto by the control member and to resist all sudden displacement bythe control member.

3. In a hydraulic system including a fluid circuit and a valve operatingmember, opposed control valves disposed in said fluid circuit on eitherside of said valve operating member, said valves being formed with aninner valve part adapted to be reciprocated by said valve operatingmember, an outer valve part surrounding the inner valve part, said outervalve part having at least one port forming a portion of said fluidcircuit, said port being situated along the line of reciprocation of theinner valve part and variably restricted thereby, said inner and outervalve parts forming a damping chamber, said chamber changing in volumeupon relative movement of said valve parts, an opening formed in one ofsaid valve parts interconnecting said chamber with the fluid circuit,yield able means disposed between the valve parts for biasing the latterin opposition to the valve actuating forces ex erted by said valveoperating member, and valve means in said opening for retarding the rateof change in volume within the chamber thereby preventing suddenmovement of the valve assembly and the valve operating member in onedirection due to the application of external forces.

4. In a hydraulic system including a fluid circuit and a valve operatingmember, Opposed control valves disposed in said fluid circuit on eitherside of said valve operating member, said valves being formed with aninner part adapted to be reciprocated by said valve operating member, anouter valve part surrounding the inner valve part, said outer valve parthaving at least one port forming a portion of said fluid circuit, saidport being situated along the line of reciprocation of the inner valvepart and variably restricted thereby, said inner and outer valve partsforming a damping chamber, said chamber changing in volume upon relativemovement of said valve parts, an opening formed in one of said valveparts interconnecting said chamber with the fluid circuit, yieldablemeans disposed between the valve parts for biasing the latter inopposition to the valve actuating forces exerted by said valve operatingmember, and a check valve in said opening for retarding the rate ofchange in volume of said chamber and for preventing sudden movement ofthe valve members and the valve operating member in one direction due tothe sudden application of external forces.

5. In a hydraulic system including a fluid circuit and a valve operatingmember, opposed control valves disposed in said fluid circuit on eitherside of said valve operating member, said valves being formed with onepart thereof adapted to be reciprocated by said valve operating member,another valve part telescopically associated with said one valve part, afirst of said valve parts having at least one port forming a portion ofsaid fluid circuit, said port being situated along the line ofreciprocation of the second valve part and variably restricted thereby,said inner and outer valve parts forming a damping chamber, said chamberchanging in volume upon relative movement of said valve parts, anopening providing communication between said chamber and said fluidcircuit, yieldable means disposed between said valve parts for biasingthe latter in opposition to the valve actuating forces exerted by saidvalve operating member, said opening being restricted upon relativemovement be tween said valve parts thereby retarding the rate of changein volume of the chamber and preventing sudden movement of the valveparts and the valve operating member upon a sudden application ofexternal forces.

6. In a hydraulic system including a fluid circuit and a valve operatingmember, opposed control valves disposed in said fluid circuit on eitherside of said valve operating member, said valves being formed with aninner part adapted to be reciprocated by said valve operating member, anouter valve part surrounding the inner valve part, one of said valveparts having at least one port forming a portion of said fluid circuit,said port being situated along the line of reciprocation of the othervalve part and variably restricted thereby, said inner and outer valveparts forming a damping chamber, said chamber changing in volume uponrelative movement of said valve parts, an opening formed in one of saidvalve parts interconnecting said chamber with the fluid circuit, a valvecooperating with said opening so as to be seated thereacross, and meansforming a passage between said chamher and said fluid circuit withprovision for progressively restricting the same during relativemovement of said valve ports throughout a range of operating positions,said passage being substantially fully open during initial relativemovement of said valve ports from a neutral position, said passagerestrictively passing hydraulic fluid therethrough and retarding therate of change in volume of the chamber thereby preventing suddenmovement of the valve parts and the valve operating member upon suddenapplication of external forces.

7. In a hydraulic system including a fluid circuit and a valve operatingmember, opposed control valves disposed in said fluid circuit on eitherside of said valve operating member, said valves being formed with onepart thereof adapted to be reciprocated by said valve operating member,another valve part telescopically associated with said one valve part,said valve parts having at least one port, a first of said valve partshaving at least one port forming a portion of said fluid circuit, saidport being situated along the line of reciprocation of the second valvepart and variably restricted thereby, said inner and outer valve partsforming a damping chamber, said chamber changing in volume upon relativemovement of said valve parts, an opening providing communication betweensaid chamber and said fluid circuit, a check valve means for controllingthe degree of restriction of said opening, and means forming a variablyrestricted passage for providing a predetermined degree of communicationbetween said chamber and said fluid circuit independently of theoperation of said check valve means.

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